Preparation Of Nickel-Cobalt Bimetal Based Electrocatalyst And The Study On Electrocatalytic Oxidation Reaction Performance

At present,the energy needed by industry mainly comes from traditional fossil fuels,which aggravate the deterioration of global environment and climate change.Therefore,it is urgent to develop clean and efficient renewable energy.Hydrogen has attracted much attention because of its high calorific value and zero emission.So far,among all techniques applied to produce hydrogen,electrocatalytic hydrolysis of water is the most ideal method of hydrogen production.However,the anodic oxygen evolution reaction（OER）in electrolytic water has a four-electron transfer mechanism and slow kinetic reaction,which seriously affects the practical application of electrolysis of water to produce hydrogen.The emergence of organic small molecules such as urea and benzyl alcohol can not only replace OER reaction,but also greatly reduce the energy consumed in electrolysis hydrogen production,and realize the purpose of purifying sewage and preparing value-added products at the same time.However,all these oxidation reactions involve multi-electron transfer mechanism,which seriously affects hydrogen production efficiency.Using electrocatalyst can accelerate the reaction and improve the energy conversion efficiency.However,the transition metal-based catalysts commonly used at present still have the shortcomings of insufficient active sites and electron conductivity,and most of the catalysts only show a single catalytic activity.Therefore,in order to further solve these problems,this thesis takes advantage of cost-effective nickel cobalt-based materials to synthesize multi-functional electrocatalysts with high catalytic activity.The specific research contents are as follows:1.Two-dimensional/three-dimensional（2D/3D）coexisting porous binary nickel-cobalt oxide solid solution（2D/3D porous Ni Co O_x/CC）was synthesized on carbon cloth by electrochemical deposition-in-situ reconstruction-pyrolysis method.The construction characterization proved the2D/3D hierarchical porous properties of the material,and X-ray powder diffraction（XRD）test confirmed that the catalyst is a mixture of Ni Co O and（Ni Co）₃O₄ solid solution.The interfacial connection between the two phases can accelerate the electron transfer rate and mass transfer.At the same time,the co-existing 2D/3D hierarchical porous structure enables the catalyst to expose more active sites in the electrolyte,thus comprehensively improving the catalytic activity and reaction kinetic behavior.In addition,the rough and porous structure can provide sufficient buffer space for the continuous redox reaction to release the stress generated by the reaction,so that the material has outstanding structure and electrochemical stability.Density functional theory（DFT）confirmed that the addition of Ni can not only adjust the electronic structure of Co O and Co₃O₄and improve the electron transport rate,but also make the d-band center away from the Fermi level,thus reducing the adsorption energy of the oxygen-containing intermediates and promoting the resolution of the oxygen-containing intermediates on the surface of the catalyst,which further speeds up the reaction process.The results of test display that the solid solution mixture has wonderful catalytic activity for urea oxidation reaction,requiring only a voltage of 1.30 V vs.RHE to reach a current density of 10 m A cm^-2,and maintaining a relatively high stability in constant voltage tests over a long period of time.Not only urea,but also this material showed good catalytic function for other organic small molecules,which confirmed the catalyst has multifunctional catalytic characteristics of the catalyst.2.Hierarchical porous nickel cobalt-base sulfide solid solution（（Ni,Co）S₂/CC）precatalyst was synthesized by electrochemical deposition-in-situ reconstruction-hydrothermal sulfidation.Scanning electron microscopy（SEM）images showed that the material also has the characteristics of hierarchical porous structure.The structural features can provide affluent active sites,sufficient stress buffer space and strong electron conductivity.X-ray photoelectron spectroscopy（XPS）showed that a more catalytically active oxide or hydroxyl oxide thin layer forms on the surface during the reaction.After constant voltage test at different time,the catalytic performance of the catalyst gradually increased.XPS combined with elemental distribution tests also testified that the catalyst surface S element gradually decreased,while the O element increased.The active species formed by polarization reaction on the surface of precatalyst has a strong catalytic capacity for urea,and its voltage is only 1.22 V vs.RHE at a current density of 10 m A cm^-2.Moreover,in the subsequent oxidation test of benzyl alcohol,the conversion rate of benzyl alcohol reached 97.50%,and the selectivity of benzoic acid was 93.78%.The Faraday efficiency（FE）is also up to 91.86%.